1. Field of the Invention
This invention relates generally to medical electrode systems. In particular, the electrodes of this invention are capable of delivering synchronized cardioversion energy pulses as well as defibrillation energy pulses to a patient. The electrodes of this invention are appropriate for use with an automatic or semi-automatic external defibrillator (xe2x80x9cAEDxe2x80x9d) as well as defibrillators capable of cardioversion.
2. Description of the Prior Art
Cardiac arrhythmias treatable with an electric shock can be further categorized as arrhythmias treated by a defibrillation energy shock or arrhythmias treated by a synchronized cardioversion energy shock. Electric shocks are typically delivered by defibrillators or cardioverters. Many devices capable of delivering a defibrillation shock are also capable of delivering synchronized cardioversion shocks. Defibrillation is typically used to treat ventricular fibrillation (xe2x80x9cVFxe2x80x9d) and pulseless ventricular tachycardia (xe2x80x9cVTxe2x80x9d), while cardioversion is typically used to treat hemodynamically stable ventricular tachycardia (xe2x80x9cVTxe2x80x9d with pulse), paroxysmal supraventricular tachycardia (xe2x80x9cPSVTxe2x80x9d), atrial fibrillation (xe2x80x9cAFxe2x80x9d) and atrial flutter. More detailed information about electrocardiography and the various types of heart rhythms may be obtained from Wagner xe2x80x9cMarriott""s Practical Electrocardiography,xe2x80x9d 9th Ed. (1994).
One frequent consequence of heart attacks is the development of cardiac arrest associated with heart arrhythmias, such as VF. This abnormal heart rhythm is caused by an abnormal and chaotic electrical activity in the heart. During VF the heart cannot pump blood effectively. VF is treated by applying a defibrillation shock to the patient""s heart through the use of a defibrillator. Defibrillation clears the heart of the abnormal electrical activity and allows the heart""s natural pacemaker areas to restore normal function. Because blood is no longer pumping effectively during VF, the chance of surviving a heart attack decreases with time after the arrest. Quick response to a heart attack by administering a defibrillating shock as soon as possible after the onset of VF is therefore often critically important.
VT is an arrhythmia originating in the ventricles, and is usually defined as having a heart rate of  greater than 100 beats/minute in an adult. VT can result in a significant health risk, since the ability of the heart to pump adequate blood is compromised. As a result, blood pressure falls. The amount of time VT can be tolerated by a patient depends on the condition of the patient and the nature of the VT, and could range from minutes to hours or days. Hemodynamically stable VT is typically treated using synchronized energy pulses known as cardioversion that are delivered in a standard sequence of, for example, 100, 200, 300 and 360 J. Although in some situations, pulses may begin with as little as 50 J. Hemodynamically unstable VT is is typically treated with unsynchronized shocks. The most current protocol information can be obtained from the American Heart Association (xe2x80x9cAHAxe2x80x9d). The protocol information described herein can be found in xe2x80x9cImproving Survival from Sudden Cardiac Arrest: The xe2x80x98Chain of Survivalxe2x80x99 Conceptxe2x80x9d Circulation 83:1832-1847 (1991).
Increasing the number of potential defibrillator operators who are trained on the proper use of an external defibrillator increases the likelihood that a trained defibrillator operator will be available during an emergency and thus could ultimately reduce the time to defibrillator deployment. As the number of potential operators increases, however, it becomes increasingly important to ensure that the defibrillator electrodes are adequately attached so that the device can receive and accurately analyze a heart rhythm signal. Accordingly, it is important to be able detect how well an electrode is attached so that the quality of therapy can be maximized, and so that electrode burns can be minimized. Traditionally, the need for detecting correct electrode attachment is balanced with the importance for quick response.
Another problem that occurs is that, inexperienced operators are more likely to fumble around in attempting to attach the electrode pads to the patient. This fumbling creates a mechanical disturbance that can result in a non-cardiac event signal being transmitted to the defibrillator along with the ECG signal of interest. As will be appreciated by those of skill in the art, signals from a mechanical disturbance are just one type of artifact signal that can corrupt the ECG signal of interest. If the ECG signal has been corrupted by artifact and the corruption is not detected and/or removed, this could result in the signal being misinterpreted. The less clinical judgment possessed by the user, the more important accurate artifact detection and/or removal becomes. Thus, as devices continue to move into the hands of lay responders, it becomes critically important that the device be able to anticipate and respond to situations where the user inadvertently creates artifact, such as a mechanical disturbance, or fails to correctly attach the electrode. None of the commercially available defibrillation or pacing electrodes are designed to address this problem. Further since the functionality of such electrodes is known in the art it will not be described herein.
What is needed is an electrode that enables the defibrillator to quickly and accurately detect and/or remove artifact from the patient and/or assess quality of pads attachment to assure optimal therapy delivery.
This invention provides a medical electrode system wherein the electrode pads are capable of improved detection of electrode attachment and improved artifact detection. Each electrode pad has a flexible substrate with an adhesive surface; two or more conductors disposed on the substrate; and two or more electrode elements disposed on the substrate and electrically connected to the conductors.
In a first embodiment, a medical electrode pad is provided. The medical electrode pad comprises a substrate with an adhesive surface; conductors in communication with the substrate; and a plurality of conductive electrode elements disposed on the substrate in a spatial relationship to each other and electrically connected to the conductors, wherein the spatial relationship of the conductors facilitates the determination of an overall electrode pad attachment quality.
In a second embodiment, the conductive electrode elements of the electrode pad may be formed so that an estimate of the degree of electrode pad contact on a patient can be calculated based on the measurement of resistance between a set of at least two of the conductive electrode pad elements. Additionally, the conductive electrode elements may be used to estimate the degree of electrode pad contact and may have an annular spatial relationship to each other. Importantly, the conductive electrode elements would be formed so that a patient skin resistivity can be calculated, independent of the degree of electrode pad contact, based on the measurement of resistance between a second set of at least two of the conductive electrode pad elements, wherein the skin resistivity is used to refine the estimate of the degree of electrode pad contact on a patient. In accomplishing the calculation of skin resistivity, the conductive electrode elements could have an annular spatial relationship to each other.
In a third embodiment, the conductive electrode elements of the electrode pad are formed so that an estimate of the degree of electrode pad contact on a patient can be calculated based on the measurement of conductance between a set of at least two of the conductive electrode pad elements. The conductive electrode elements have an annular spatial relationship to each other and are used to estimate the degree of the electrode pad contact. The conductive electrode elements could be formed so that a patient skin conductivity can be calculated, independent of the degree of electrode pad contact, based on the measurement of conductance between a second set of at least two of the conductive electrode pad elements. The skin conductivity is then used to refine the estimate of the degree of electrode pad contact on a patient. The conductive electrode elements used to calculate the patient skin conductivity may have an annular spatial relationship to each other.
In a fourth embodiment of the invention, the conductive electrode elements are formed so that an artifact reference signal can be detected based on the measurement of a differential voltage between a set of at least two of the conductive electrode pad elements.
Several methods may be employed to operate the invention. In a first method of the invention, the electrode pad of the invention is used by: applying an electrode pad having a plurality of conductive electrode elements to a patient; and then determining a pad attachment quality for an electrode pad based on a measured resistance between a first and second conductive element, the gap width between the first and second conductive electrode element, the effective perimeter of the gap between the second and third electrode element, and a typical skin resistivity value.
In a second method of using the invention, a medical electrode pad is used by: applying an electrode pad having a plurality of conductive electrode elements to to a patient; calculating a patient""s local skin resistivity based on a measured resistance between a first and second conductive element, the gap width between the first and second conductive electrode element, and the effective perimeter of the gap between the first and second electrode element; and then determining a pad attachment quality for an electrode pad based on the local skin resistivity so calculated, the gap width between a third and fourth conductive electrode element, the measured resistance between the third and fourth conductive element and the effective perimeter of the gap between the third and fourth electrode element. Further, one of the first and second electrode elements, and one of the third and fourth electrode elements could comprise the same element.
In a third method of using the invention, a medical electrode pad is used by: applying an electrode pad having a plurality of conductive electrode elements to a patient; and then determining a pad attachment quality for an electrode pad based on a measured conductance between a first and second conductive element, the gap width between the first and second conductive electrode element, the effective perimeter of the gap between the second and third electrode element, and a typical skin conductivity value.
In a fourth method of using the invention, a medical electrode pad is used by: applying an electrode pad having a plurality of conductive electrode elements to a patient; calculating a patient""s local skin conductivity based on a measured conductance between a first and second conductive element, the gap width between the first and second conductive electrode element, and the effective perimeter of the gap between the first and second electrode element; and then determining a pad attachment quality for an electrode pad based on the local skin conductivity so calculated, the gap width between a third and fourth conductive electrode element, the measured conductance between the third and fourth conductive element and the effective perimeter of the gap between the third and fourth electrode element. Further, one of the first and second electrode elements, and one of the third and fourth electrode elements could comprise the same element.
In a fifth method of using the invention, a medical electrode pad is used by: applying an electrode pad having a plurality of conductive electrode elements to a patient; and then calculating an artifact reference signal based on a differential voltage value between at least two of the plurality of conductive electrode elements.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments, and from the claims.